Solar boosting experiment

[Phssthpok]

Since I need to wait a few weeks before wiring my new (to me) KC80's into my array (system is currently located about 120 miles away), I decided to try a few experiments. We had full sun today, no clouds and high 70degree temps...so good conditions.

I situated the panel as best I could for best alignment and hooked up the muli-meter.

I then used a small mirror (approx 8"x10") to reflect a little extra sun onto the panel. Since the light footprint was only approx. 10% of the surface area of the panel I wasn't expecting much, and thats about what I got....about .01 increase in volts, and about the same in amperage (.01A). Conclusion for this wholly un-imperical experiment are that using mirrors WILL increas output, though it may be so little as to not be worth the effort.

The interesting part came when the readings jumped up to an added .03-.04 in voltage when the light patch passed over a particular patch of cells. I passed the light over the entire panle and it was just in this one isolated patch where the readings jumped like that. Odd.

Another experiment I ran dealt with what I had heard about just a small patch of shade affecting output. Using the aforementioned mirror I passed the patch of shadow over the panel while observing the output. What suprised me what that ouput wasn't affected in the slightest UNTILL  I 'bridged' the two center rows of cells with the shadow.....then the output dropped to about 1.5Amps (normal is about 4.74Amps). I thought maybe it was because I 'bridged' the two riows of cells and tried to replicate teh results on the outer two rows (on both sides) with no effect. Now the way everyone was talking, the output should dump the moment a certain percentage of panel is shaded....at ANY spot.

Thoughts?

[Countryboy]

Hi,

It's my understanding that a series of cells will only flow the max current of the weakest cell.

If the shaded cell is the cell in the beginning of the series, it may not reduce amperage very much because it doesn't restrict the current from the other cells.  if you shaded the cell at the end of the series, it may restrict the current flowing from the other cells.  The shade on one cell may make all cells prior to that cell as weak as the shaded cell.

When using the mirror to add light, try to think of it from a different perspective.  Try to think of the whole panel being shaded, except for the spot that has the extra light from the mirror.  The very last cell in the series is the only cell capable of flowing a higher current, because there are no shaded cells past it to restrict current.

That's my best guess.

[SamoaPower]

Huuuh!

[TomW]

Country;

If the shaded cell is the cell in the beginning of the series, it may not reduce amperage very much because it doesn't restrict the current from the other cells.  if you shaded the cell at the end of the series, it may restrict the current flowing from the other cells.  The shade on one cell may make all cells prior to that cell as weak as the shaded cell.

Just a [minor] point.

Any cell in a sereies "string" of cells that produces low current will limit the whole string. First, Middle or Last. They are all in series so it has to be thought of as a whole. So it makes no difference if it is first or last or any point in the string. Same effect.

Just had to point that out. Circuits 101 stuff.

Cheers.

TomW

[finnsawyer]

An outfit in Australia called Sun Ball was posting a while back concerning their solar product that used a one meter or so Fresnel lens to concentrate the sun's power on a solar array.  It looked like a good idea, but didn't produce enough power for this greedy guy.  I suggested they put seven of the units together with one drive and one controller.  That would be about three meters or ten feet in diameter.  Should be some savings due to the larger scale.  Haven't heard anything since.  That might be something I would be interested in buying.  We get about sixteen hours of sun in the summer here at 47 degrees north latitude, but the unit must be able to track the sun for the entire time.  I'd have to put it in a shelter of some king to protect it from the 250 inches of snow we get.  But summer solar, winter wind power makes sense to me for this area.

[powerbuoy]

I do not think that one or two extra mirrors will do the trick ... you'll need "MANY" mirrors to see an effect. A better way may be to place copper tubing arrays on the back of the solar panel and use that water circuit for home water heating. Your efficiency will go up, maybe you'll even lower the panels resistance since you're draining heat away ...

Powerbuoy

[altosack]

Tom,

Any cell in a sereies "string" of cells that produces low current will limit the whole string

That's what I always thought, because that's what the experts told me, and it made sense when I though about it.  However, after actually installing some panels and observing them, it seems that when shaded, it only loses amps in about direct proportion to the area that's shaded.  It also has a lot to do with how far away the shading object is; if it's far, and the shade lines are not sharp, the decrease is much less (you can see some insolation in the shade).

Doing the same experiments as above, I have yet to get the results I expect and have been told to expect.

Dave

[dinges]

I don't see the relevance of your response to Tom's quote.

You say that reduction in current of a PV sytem is dependent on the amount of shadow on the panels. Correct.

But any cell that receives that shadow, whether it's in the middle, the beginning or the end of a series string, will limit the total current by the same amount. That's the basic characteristic of series circuits: the current in the entire loop is the same for each PV panel. Basic electric circuit theory.

Peter.

[altosack]

Peter,

You're right, I wasn't clear and wasn't really responding directly to Tom's post.  I agree with what you and Tom say about it not making any difference which cell is shaded in the string, and I wasn't trying to reply to that (even if that's what I wrote !).  I seem to have read more into the story/posts than was there because of my experiences, but didn't let you in on what was in my head.

My point was (and maybe you can set me straight if I don't understand it), that, according to what I understand of the theory, if one cell is completely shaded, then it should have a current near zero, giving the whole string (probably either the whole panel, or 1/2 the panel if it's a big one) a current near zero. I've seen this quoted by solar experts, including at Home Power magazine. However, in my experience, and from the first post, it doesn't seem to be the case, and the current just reduces in approximate proportion to the area shaded.

Presumably, the voltage reduces, too, but since I don't have a MPPT solar controller and didn't measure it, I couldn't tell.

Dave